a. Field of the Invention
The present invention relates to a safety anchor device for limiting the movement of a person or arresting a fall of a person working at height, and in particular to an inflatable safety anchor that may be positioned on a roof or other high point and then inflated with a liquid such as tap water to provide a dead-weight anchor device.
b. Related Art
Dead-weight anchor systems, also known as anchor-weight systems, are used when people need to work at height, usually on a roof or a similar structure, and a preinstalled fixed anchor system is not available. A fixed anchor system might not be available because an anchor system has never before been needed at a work location or because there is some difficulty in installing a fixed anchor system or because access is only needed temporarily. A dead-weight anchor system therefore uses an anchor device that can be moved into position and then weighted down to provide a dead-weight anchor.
Dead-weight anchor systems are ideal for flat roofs where no roof penetration is possible, but may be used on any flat or gently sloping surface where the slope is insufficient to destabilise the dead-weight anchor. Examples of other locations include lift-shaft housings on tower blocks, exposed balconies, large beams or sound areas of concrete and geological features.
One type of dead-weight anchor system uses a metal frame with a central eye bolt anchorage point with a centre swivel in an upper surface of the frame. After positioning, the frame may be loaded with weights until the dead-weight anchor has sufficient mass to resist movement when limiting the movement of a person or when arresting a fall of a person working at height connected to the anchor by a safety rope or line. The relevant standard governing dead-weight anchor systems is BS EN 795:1997 and the Code of Practice for their use is BS 7883.
The strength of the attachments to the dead-weight anchor device should at least equal the strength of the rope(s) attached to the safety anchor.
Dead-weight anchor devices themselves should be unquestionably reliable. Wet conditions can significantly affect the frictional performance of dead-weight anchor systems. The frictional resistance of any dead-weight anchor device should be assured by being capable of not moving when subjected to a load of four times that which will be applied when limiting the movement of a person in a work positioning situation. A higher factor will be required if the dead-weight anchor system may be needed to arrest a fall of a person working at height. It may also be necessary to consider the possibility of rescue, which may involve the weight of two persons.
One type of dead-weight anchor device uses an inflatable flexible anchor bag that is positioned for use when empty, and then filled with a liquid, which will normally be tap water, for example by means of a hose. When inflated with water the flexible anchor bag serves as a dead-weight anchor device. The bag may have an inlet to which the hose is temporarily connected when being filled with water. The inlet may also serve as an outlet to drain water when the device is not in use. It is important to have sufficient contact area and mass to provide sufficient friction between a lower side of the device and the supporting surface. To ensure that the lower side remains flat and to provide maximum weight, the flexible anchor bag has an approximately cubic form when inflated with water.
The flexible bag necessarily has flexible walls so that the bag can be collapsed when not in use and expanded when filled with water. This causes a problem when the attachment point is provided on the top surface, as a pull on the bag can cause the anchor bag to roll as the flexible walls deform from the pulling force. To reduce this problem, the safety line or working line attachment are therefore preferably provided on a side of the bag, however, this results in a restriction in the working area that may be covered by a worker working at height, as the safety line or working line should always lead directly to the attachment point and should not be wrapped around the dead-weight anchor device.
It is an object of the present invention to provide a more convenient dead-weight anchor bag for use on a roof or other exposed location at height.